A number of processes are known for obtaining a fiber from two or more incompatible polymer components, whereby the polymer components may be distributed over the fiber cross-section in many different ways. Also, various methods have been tried to separate the components of multicomponent fibers after spinning.
Okamoto in an article entitled "Ultra-Fine Fiber and Its Application", Japan Textile News, November 1977, pp. 94-97 and December 1977, pp. 77-81, summarized known techniques for making fine-denier fibers and in particular, the ultra-conjugate (converging) fiber spinning method (Integral Fiber's Method). The fiber produced is described as having "islands-in-a-sea".
U.S. Pat. No. 3,531,368 illustrates the details of several types of nozzles referred to in the aforesaid Okamoto article and describes a process for the manufacture of a matrix microfilament yarn wherein a great many very fine microfilaments (segments) of component A are surrounded by a matrix component B and separated from each other by the latter. This type of structure is obtained by first pre-molding bicomponent structures material is simultaneously forced into each segment formed by the above mentioned radial thin layers and the wall of the line, to embed the above mentioned thin streams between the stream of the latter spinning material. Finally, the combined stream is extruded through the discharge opening without disrupting the flow line of the thin layer. Although FIGS. 1-6 of this patent illustrate cross-sections with segments from three to six, the production of filaments with three and five or more segments (with the exception of six segments) is difficult. Moreover, the spinning heads described in this patent are also difficult to make and conversion of the spinning heads from one cross-section to another, for example from four segments to six segments, matrix and segment filaments is not described; rather, this patent merely teaches one to dissolve or decompose one of them with water or organic solvents.
In U.S. Pat. No. 3,540,080, a great many yarn cross-sections having more than two segments composed of different polymer components are disclosed. All segments are composed of different polymer components, not separated by a matrix component. Moreover, most the yarn cross-sections are encased in the matrix component. Although it is the objective of many recent developments in the field of multicomponent yarns, these yarns cannot be separated by mechanical and/or chemical aftertreatment into a yarn bundle composed of extremely fine filaments and/or fibers.
In British Pat. No. 1,104,694, fine denier filaments are obtained from matrix-fibril filaments by preliminary treatment of the matrix-fibril filaments, e.g. by treatment with heat, solvents or swelling agents followed by flexural stressing. However, this process results in filaments with only a partial and very uneven fibrillation. Textile sheet structures obtained from such filaments are of limited use and lack the desired softness and the required silk-like luster. Moreover, they leave much to be desired in terms of covering power.
U.S. Pat. No. 3,966,865 teaches the manufacture of textile fiber structures from multicomponent filaments of polyamide and other polymers by using for fibrillation an aqueous emulsion of 1.5 to 50 wt. % benzyl alcohol and/or phenylethyl alcohol obtained by means of a surfactant. A prereequisite is that the treatment solution transmits less than 20% of the light having a wavelength of 495 nm. One drawback of this process is that the composition of the treatment agent as well as the treatment conditions must be accurately controlled. It is extremely difficult to obtain a specific degree of fibrillation with this process; frequently, the fibrillation of the filament is only incomplete. Also, the textile sheet structure must be subjected to a relatively long treatment to induce any appropriate fibrillation. This treatment causes the fibers to readily stick to one another. There is also the risk of chemical modification of polyamides during treatment so that the end product no longer has the required characteristics.
Similar processes are also described in U.S. Pat. No. 4,073,988 which mentions a series of other organic solvents used as solutions or emulsions in water. Essentially the same drawbacks are experienced with these procedures as mentioned above in connection with U.S. Pat. No. 3,966,865. Furthermore, considerable difficulties are experienced in processing aqueous solutions of emulsions containing organic solvents; the recovery of pure organic solvents for further use is not only complex, but there are various problems in water decontamination with are significant especially in terms of antipollution.
U.S. Pat. No. 3,117,362 describes the treatment of multicomponent fibers with acetone. Although the filaments are treated fro five minutes in the solvent, there was no significant separation and only partial splitting is achieved when drawing the filament over a sharp edge. Complete splitting was only achieved after repeating such mechanical aftertreatment three times.
Although a number of methods for splitting multicomponent fibers and obtain corresponding fiber structures are known, there is still a need for improved processes leading to fiber structures having better properties. Accordingly, an object of the invention is to provide a process permitting the manufacture of fiber structures by splitting of multicomponent fibers simply, economically and reproducibly to a specific, desired degree of splitting.
Another object is to provide filaments that can be completely separated giving a uniform bundle structure distinguished by a very fine denier, a soft, silk-like hand, a high covering power having many varied applications in the textile and industrial sector.
An object of the invention is to provide patterned, dyeable knit goods characterized by variations in optical transparency or relief effects having a very pleasing appearance and a pleasant soft textile hand and excellent drape.
Another object of the invention is to provide a web characterized by an especially high density and uniformity, high covering power and good tenacity and particularly by a high degree of mutual matting of the fibers which may further be bonded at the points of intersection of segments and/or matrix fibers.